Re-awakening heresiarch spawns additional halo cubes
From DoomWiki.org
Under vanilla Hexen, a heresiarch that returns to its idle state and then re-awakens will spawn an additional set of mana halo cubes with each re-awakening, which, due to the special relationship between these entities, causes altered behavior. The most immediately visible effect is that the heresiarch's spell casting speed becomes faster with each re-awakening, eventually becoming nearly instantaneous in extreme cases. The attack where the heresiarch fires a wave of purple projectiles is also bolstered, sometimes forming a double helix pattern. When killed, the dying heresiarch will release all the additional sets of cubes into their bouncing explosion routine.
The bug is somewhat rare, as it requires specific circumstances in order to occur, and may be more apparent in certain PWAD setups than in the unmodified game. In order to fall asleep once awakened, the heresiarch must be distracted from targeting the player in some way, and infights involving heresiarchs are subject to several restrictions. Under normal circumstances, while a player is alive, no monster can intentionally target a heresiarch, so the infight must be instigated by crossfire hitting the heresiarch while it is vulnerable. Summoned maulotaurs or dark bishops also do not work. An infight may also be possible under special circumstances if the player has died.
